The present invention relates to a process for monitoring the gas volume in an hydropneumatic accumulator by measuring the volume increase of the hydraulic fluid following a pressure increase occuring at a given minimum pressure, by measuring the hydraulic pressure and by a signal output as a function of the volume and pressure increases at insufficient gas volumes.
In a process of this kind, known, for example, from DE-PS No. 15 25 857, the volume of gas in the accumulator is indirectly derived from the filling quantity and the pressure increase. In this process, either the largest permissible pressure difference associated with a given filling quantity or the smallest permissible filling quantity associated with a given pressure difference is determined.
In another process, known for example from DE-OS No. 22 40 394, a minimum gas volume is set by an internal stop in the accumulator for the purpose of monitoring the gas indirectly. If on refilling a free running piston drives against this stop, then the pump delivers, so to speak, against a solid wall and generates a steep pressure increase. In this process, conclusions concerning the volume of gas in the accumulator are drawn indirectly from the value for the pressure. In the known models, temperature compensation of the measuring values triggering the signal are not provided. Rather, in all applications of hydropneumatic accumulators, the minimum gas volume is calculated with respect to the lowest temperature of the environment respectively of the gas to be expected. This minimum gas volume limited by the piston position given on loading and unloading of the accumulator, is, however, different at different ambient temperatures, which therefore can possibly trigger temperature-related error signals during gas monitoring of hydropneumatic accumulators.